An aerofoil is a structure with a curved shape, like a wing, designed to generate lift when it moves through a fluid such as air. Its primary application is in aviation, enabling airplanes to fly.

The flight of an aircraft is governed by four primary forces. For stable flight, lift must balance weight, and thrust must balance drag.

Working Principle

The generation of lift is primarily explained by two principles:

1. Bernoulli's Principle: The curved upper surface of the aerofoil forces air to travel a longer distance than the air flowing under the flatter bottom surface. This means the air on top moves faster. According to Bernoulli's principle, faster-moving air has lower pressure. This pressure difference between the lower (high pressure) and upper (low pressure) surfaces creates a net upward force: lift.

For more details on Bernoulli's principle, refer to Bernoulli's Equation→.

The lift force can be calculated as:

$F_L=(P_1-P_2)\times A$

where $P_1$ is the pressure on the lower surface, $P_2$ is the pressure on the upper surface, and $A$ is the wing area.

2. Newton's Third Law: The aerofoil is angled to deflect air downwards. According to Newton's Third Law (for every action, there is an equal and opposite reaction), as the wing pushes air down, the air pushes the wing up.

Angle of Attack and Stalling

• Angle of Attack (AOA): This is the angle between the aerofoil's chord line (an imaginary line from its leading to trailing edge) and the direction of the oncoming air.

• Effect on Lift: Increasing the AOA generally increases lift, but only up to a certain point.

• Stall: If the AOA becomes too high (the critical angle of attack), the airflow separates from the upper surface of the aerofoil. This causes a drastic reduction in lift and an increase in drag, a condition known as a stall.

Spin Bowling and the Magnus Effect

In cricket, when a bowler imparts spin on the ball, it deviates from a straight path as it travels through the air. This curving motion is caused by the Magnus effect, which is the result of the interaction between the spinning ball and the surrounding air.

The Magnus Effect Explained

1. Spin and Airflow: A spinning ball drags a thin layer of air with it. On one side of the ball, this layer of air moves in the same direction as the airflow, causing the air to speed up. On the opposite side, it moves against the airflow, slowing it down.
2. Pressure Difference: According to Bernoulli's Principle, the faster-moving air on one side creates a region of lower pressure, while the slower-moving air on the other side creates a region of higher pressure.
3. Lateral Force: This pressure difference generates a net force on the ball, pushing it from the high-pressure side to the low-pressure side. This force is perpendicular to both the direction of the ball's motion and the axis of its spin, causing it to curve or "drift" sideways.

Types of Spin in Cricket

The direction of drift and subsequent turn off the pitch depends on the spin axis.